Centrifugal compressor

ABSTRACT

A centrifugal compressor includes a housing, a rotary shaft accommodated in the housing, an electric motor including a motor rotor and a motor stator for rotating the rotary shaft, an impeller connected to one end of the rotary shaft and driven by rotation of the rotary shaft so as to compress fluid, a radial bearing rotatably supporting the rotary shaft in a radial direction of the rotary shaft, and a resolver including a resolver rotor and a resolver stator for detecting a rotation angle of the motor rotor. The resolver rotor is fixed to the other end of the rotary shaft opposite to the impeller. The rotary shaft includes a radial support member rotatably supported by the radial bearing, and a radius of the radial support member is larger than a radius of gyration of the resolver rotor.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2018-109452 filed on Jun. 7, 2018, the entire disclosure of which is incorporated herein by reference.

BACKGROUND ART

The present disclosure relates to a centrifugal compressor.

Some of vehicles in recent years mount a fuel cell system having a fuel cell stack that generates electricity by chemically reacting hydrogen as fuel gas with oxygen in air as oxidant gas. Japanese Patent Application Publication No. 2010-144537 discloses an example of a fuel cell system including a centrifugal compressor for compressing the air to supply to a fuel cell stack. The centrifugal compressor includes a housing, a rotary shaft accommodated in the housing, an electric motor accommodated in the housing for rotating the rotary shaft, an impeller connected to one end of the rotary shaft and driven by rotation of the rotary shaft so as to compress air, and radial bearings that rotatably support the rotary shaft in a radial direction of the rotary shaft in relation to the housing. The electric motor includes a motor rotor fixed to the rotary shaft and a motor stator fixed to the housing. In order to detect a rotation angle of the motor rotor of the electric motor, a resolver is used, like an example disclosed in Japanese Patent Application Publication No. 2017-158395. The resolver includes a resolver rotor fixed to the rotary shaft and a resolver stator fixed to the housing.

When a resolver is provided to a rotary shaft of a centrifugal compressor, the rotary shaft may easily lose its rotating balance that may cause a runout, since a rotary shaft of a centrifugal compressor rotates at a high speed of, for example, 80,000 rpm or more.

In some of centrifugal compressors, a resolver is disposed at an end opposite to an impeller in an axial direction of a rotary shaft in relation to a housing in consideration of resolver wiring drawn out of a resolver stator coil in the housing. In this case, a resolver rotor is fixed to the rotary shaft at the other end opposite to the impeller. In a case where the resolver rotor is fixed to the rotary shaft before the rotary shaft is assembled into the housing, the resolver rotor may interfere with the radial bearing during assembly of the rotary shaft, which may fail to assemble the rotary shaft into the housing. For this reason, the resolver rotor is fixed to the rotary shaft at the other end opposite to the impeller after assembly of the rotary shaft into the housing.

Supposing a case where an imbalance in the weight distribution is corrected with the motor rotor fixed to the rotary shaft in the circumferential direction of the motor rotor so as to adjust the rotating balance of the rotary shaft prior to assembly of the shaft into the housing, the resolver rotor would be fixed to the rotary shaft after assembly of the rotary shaft into the housing. In this case, the rotating balance of the rotary shaft adjusted by correcting the imbalance in the weight distribution in the circumferential direction of the motor rotor would be lost by addition of the resolver rotor to the rotary shaft after assembly of the rotary shaft into the housing, which could easily cause a runout of the rotary shaft.

The present disclosure has been made in view of the above circumstances and is directed to providing a centrifugal compressor that suppresses a runout of the rotary shaft.

SUMMARY

In accordance with an aspect of the present disclosure, there is provided a centrifugal compressor. The centrifugal compressor includes a housing, a rotary shaft accommodated in the housing, an electric motor having a motor rotor fixed to the rotary shaft and a motor stator fixed to the housing for rotating the rotary shaft, an impeller connected to one end of the rotary shaft and driven by rotation of the shaft so as to compress fluid, a radial bearing rotatably supporting the rotary shaft in a radial direction of the shaft in the housing, and a resolver having a resolver rotor fixed to the rotary shaft and a resolver stator fixed to the housing for detecting a rotation angle of the motor rotor. The resolver rotor is fixed to the other end of the rotary shaft opposite to the impeller. The rotary shaft includes a radial support member rotatably supported by the radial bearing, and a radius of the radial support member is larger than a radius of gyration of the resolver rotor.

Other aspects and advantages of the disclosure will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:

FIG. 1A is a schematic diagram of a fuel cell system according to a first embodiment of the present disclosure;

FIG. 1B is a front view of a resolver rotor according to the first embodiment of the present disclosure;

FIG. 2A is a view diagrammatizing a state before assembly of a rotary shaft into a housing according to the first embodiment of the present disclosure;

FIG. 2B is a view diagrammatizing a state after assembly of the rotary shaft into the housing according to the first embodiment of the present disclosure;

FIG. 3 is a schematic diagram of a fuel cell system according to a second embodiment of the present disclosure;

FIG. 4A is a view diagrammatizing a state before assembly of a rotary shaft into a housing according to the second embodiment of the present disclosure; and

FIG. 4B is a view diagrammatizing a state after assembly of the rotary shaft into the housing according to the second embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS First Embodiment

The following will describe a centrifugal compressor according to a first embodiment of the present disclosure with reference to FIGS. 1A to 2B. The centrifugal compressor compresses air as oxidant gas, that is, fluid to supply to a fuel cell stack of a fuel cell system. The fuel cell system according to the first embodiment is mounted on, for example, a fuel-cell vehicle.

As shown in FIG. 1A, a fuel cell system 10 includes a fuel cell stack 11 and a centrifugal compressor 12 for compressing air. The air compressed by the centrifugal compressor 12 is supplied to the fuel cell stack 11. The fuel cell stack 11 includes, for example, a plurality of cells. Each of the cells is configured by laminating an oxygen electrode, a hydrogen electrode, and an electrolyte membrane disposed therebetween. The fuel cell stack 11 generates electricity by chemically reacting hydrogen as fuel gas with oxygen in air. For oxidant gas, any gas containing oxygen may be used.

The fuel cell stack 11 is electrically connected to an unshown vehicle-driving motor. The vehicle-driving motor is driven by electric power generated by the fuel cell stack 11. The power for the vehicle-driving motor is transmitted to vehicle axle through an unshown power transmission mechanism. Then, the vehicle travels at a speed depending on an opening degree of an accelerator pedal.

Oxygen used to generate power in the fuel cell stack 11 constitutes only approximately 20% in air. Approximately 80% of air supplied to the fuel cell stack 11 is exhausted as exhaust gas from the fuel cell stack 11 without being used for generating power for the fuel cell stack 11.

The fuel cell stack 11 includes a supply port 11 a supplying air, an exhaust port 11 b exhausting air as exhaust gas, and an air passage 11 c connecting the supply port 11 a to the exhaust port 11 b. In the air passage 11 c, the air supplied from the supply port 11 a flows towards the exhaust port 11 b.

The centrifugal compressor 12 includes a housing 13, a rotary shaft 14 accommodated in the housing 13, an electric motor 15 accommodated in the housing 13 for rotating the rotary shaft 14, and an impeller 16 connected to the rotary shaft 14 accommodated in the housing 13 and driven by rotation of the rotary shaft 14 so as to compress the air. The impeller 16 is connected to one end or a first end of the rotary shaft 14 so as to rotate integrally with the rotary shaft 14. The rotary shaft 14 of the centrifugal compressor 12 rotates at a high speed of, for example, 80,000 rpm or more.

The electric motor 15 includes a tubular motor rotor 17 fixed to the rotary shaft 14 and a tubular motor stator 18 fixed to the housing 13. The motor rotor 17 is disposed inside the motor stator 18 and rotates integrally with the rotary shaft 14. The motor rotor 17 includes a cylindrical motor rotor core 17 a fastened to the rotary shaft 14 and a plurality of unshown permanent magnets provided to the motor rotor core 17 a. The motor stator 18 surrounds the motor rotor 17. The motor stator 18 includes a cylindrical motor stator core 18 a fixed to the housing 13 and a coil 18 b wound around the motor stator core 18 a. The motor rotor 17 rotates integrally with the rotary shaft 14 when electric current flows from an unshown battery to the coil 18 b. Then, the impeller 16 rotates integrally with the rotary shaft 14 so as to compress the air.

The housing 13 includes a suction port 13a for sucking air and a discharge port 13 b for discharging the air. In addition, the fuel cell system 10 has a passage 20 a for the centrifugal compressor 12. The passage 20 a is formed by, for example, a pipe. One end of the passage 20 a is open to the atmosphere, whereas the other end of the passage 20 a is connected to the suction port 13 a. The external air flows through the passage 20 a to be sucked into the suction port 13 a, The impeller 16 compresses the air sucked into the suction port 13 a. Then, the air compressed by the impeller 16 is discharged from the discharge port 13 b.

The fuel cell system 10 has a supply passage 20 b connecting the centrifugal compressor 12 to the fuel cell stack 11. The supply passage 20 b is formed by, for example, a pipe. One end of the supply passage 20 b is connected to the discharge port 13 b, whereas the other end of the supply passage 20 b is connected to the supply port 11 a. The air discharged from the discharge port 13 b flows through the supply passage 20 b to be supplied to the supply port 11 a.

The fuel cell system 10 has an exhaust passage 20 c. The exhaust passage 20 c is formed by, for example, a pipe. One end of the exhaust passage 20 c is connected to the exhaust port 11 b, whereas the other end of the exhaust passage 20 c is open to the atmosphere. The exhaust gas exhausted from the exhaust port 11 b flows through the exhaust passage 20 c to be exhausted into the atmosphere.

The centrifugal compressor 12 includes a first radial bearing 21 and a second radial bearing 22 as tubular radial bearings for rotatably supporting the rotary shaft 14 in a radial direction of the rotary shaft 14 in the housing 13. In the first embodiment of the present disclosure, the first radial bearing 21 and the second radial bearing 22 are disposed at the rotary shaft 14 in an axial direction so as to sandwich the electric motor 15. The first radial bearing 21 is located at a side closer to the impeller 16 than the electric motor 15, whereas the second radial bearing 22 is located at a side opposite to the impeller 16 relative to the electric motor 15,

The rotary shaft 14 includes a first radial support member 14 a as a cylindrical radial support member rotatably supported by the first radial bearing 21. The rotary shaft 14 also includes a second radial support member 14 b as a cylindrical radial support member rotatably supported by the second radial bearing 22. The first radial support member 14 a and the second radial support member 14 b are provided at the rotary shaft 14 at the side so as to sandwich the electric motor 15 The first radial support member 14 a and the second radial support member 14 b are part of the rotary shaft 14 and rotate integrally with the rotary shaft 14. The first radial bearing 21 surrounding the first radial support member 14 a is fixed to the housing 13, whereas the second radial bearing 22 surrounding the second radial support member 14 b is fixed to the housing 13. An outside diameter R1 of the first radial support member 14 a is identical with an outside diameter R2 of the second radial support member 14 b, In other words, the radius of the first radial support member 14 a is identical with the radius of the second radial support member 14 b.

The first radial bearing 21 supports the rotary shaft 14 in contact with the first radial support member 14 a until a rotational speed of the electric motor 15 (the rotary shaft 14) reaches a predetermined value while the second radial bearing 22 supports the rotary shaft 14 in contact with the second radial support member 14 b until the rotational speed of the electric motor 15 reaches the predetermined value. Then, when the rotational speed of the electric motor 15 :30 reaches the predetermined value, the first radial support member 14 a floats in relation to the first radial bearing 21 owing to a dynamic pressure generated between the first radial support member 14 a and the first radial bearing 21 so that the first radial bearing 21 supports the rotary shaft 14 out of contact with the first radial support member 14 a. Likewise, when the rotational speed of the electric motor 15 reaches the predetermined value, the second radial support member 14 b floats in relation to the second radial bearing 22 owing to a dynamic pressure generated between the second radial support member 14 b and the second radial bearing 22, so that the second radial bearing 22 supports the rotary shaft 14 out of contact with the second radial support member 14 b.

The centrifugal compressor 12 includes flat ring-shaped thrust bearings 23 rotatably supporting the rotary shaft 14 in the axial direction of the rotary shaft 14 in relation to the housing 13. Two pieces of the thrust bearings 23 are disposed at positions closer to the impeller 16 than the electric motor 15 in the axial direction of the rotary shaft 14 between the first radial bearing 21 and the impeller 16. The two thrust bearings 23 are supported by the housing 13.

The rotary shaft 14 includes a flat ring-shaped thrust support member 24 rotatably supported by the two thrust bearings 23. The thrust support member 24 is provided to the rotary shaft 14 disposed between the impeller 16 and the first radial support member 14 a. The thrust support member 24 is sandwiched by the two thrust bearings 23 in the axial direction of the rotary shaft 14. Thus, the two thrust bearings 23 are disposed so as to sandwich the thrust support member 24 in the axial direction of the rotary shaft 14. In the first embodiment of the present disclosure, the thrust support member 24 is a ring-shaped element that is provided separately from the rotary shaft 14. The thrust support member 24 is fixed by, for example, press-fitting into the rotary shaft 14 so as to rotate integrally with the rotary shaft 14.

The thrust bearing 23 supports the rotary shaft 14 in contact with the thrust support member 24 until the rotational speed of the electric motor 15 (the :30 rotary shaft 14) reaches a predetermined value. Then, when the rotational speed of the electric motor 15 reaches the predetermined value, the thrust support member 24 floats in relation to the thrust bearings 23 owing to a dynamic pressure generated between the thrust support member 24 and each of the thrust bearings 23 so that the thrust bearings 23 supports the rotary shaft 14 out of contact with the thrust support member 24.

The centrifugal compressor 12 includes a resolver 30 for detecting a rotation angle of the motor rotor 17. The resolver 30 includes a tubular resolver rotor 31 fixed to the rotary shaft 14 and a tubular resolver stator 32 fixed to the housing 13.

The resolver rotor 31 is fixed to the other end or a second end of the rotary shaft 14 opposite to the impeller 16. In the first embodiment of the present disclosure, there arranged are the impeller 16, the thrust support member 24, the first radial support member 14 a, the motor rotor core 17 a, the second radial support member 14 b, and the resolver rotor 31, in this order, from the one end or the first end towards the other end or the second end of the rotary shaft 14. Therefore, the thrust support member 24 is disposed closer to the impeller 16 than the resolver rotor 31, the motor rotor 17, the first radial support member 14 a, and the second radial support member 14 b in the axial direction of the rotary shaft 14.

The resolver rotor 31 is disposed inside the resolver stator 32 and rotates integrally with the rotary shaft 14. The resolver stator 32 surrounds the resolver rotor 31. The resolver stator 32 includes a tubular resolver stator core 32 a fixed to the housing 13 and a coil 32 b wound around the resolver stator core 32 a. A resolver wire 32 c is drawn out of the coil 32 b of the resolver stator 32. The resolver wire 32 c is electrically connected to an unshown control unit. When the resolver rotor 31 rotates, rotation of the resolver rotor 31 is detected so that a two-phase resolver signal is output from the coil 32 b through the resolver wire 32 c to the control unit.

The control unit computes a target current value based on the resolver signal so that the rotational speed of the electric motor 15 becomes equal to a target motor speed. The target motor speed is a rotational speed command value, which is determined in accordance with a power generation output required for the fuel cell stack 11 based on aspects of accelerator pedal operation and others. The rotational speed command value is sent to the control unit from the fuel cell system 10. Then, the control unit controls the rotational speed of the electric motor 15 so as to be the target motor speed for driving the electric motor 15.

As shown in FIG. 1B, the resolver rotor 31 has an insertion hole 31a through which the rotary shaft 14 is inserted. The shape of the insertion hole 31 a is a perfect circle. The axis of the insertion hole 31 a aligns with an axial center L1 of the rotary shaft 14. Therefore, the insertion hole 31 a is a circular hole centering around the axial center L1 of the rotary shaft 14.

A periphery of the resolver rotor 31 has a farthest portion 31 b that is a portion the most distanced from the axial center L1 of the rotary shaft 14 in the radial direction of the rotary shaft 14 and a closest portion 31 c that is a portion the least distanced from the axial center L1 of the rotary shaft 14 in the radial direction of the rotary shaft 14. The farthest portion 31 b and the closest portion 31 c are spaced apart circumferentially by 180 degrees from each other. A radius of the periphery of the resolver rotor 31 from the axial center L1 of the rotary shaft 14 gradually decreases from the farthest portion 31 b towards the closest portion 31 c, which forms an imperfect circle. Therefore, the farthest portion 31 b is a portion having the largest radius of the periphery of the resolver rotor 31 from the axial center L1 of the rotary shaft 14, whereas the closest portion 31 c is a portion having the smallest radius of the periphery of the resolver rotor 31 from the axial center L1 of the rotary shaft 14. The thickness of the resolver rotor 31 decreases gradually from the farthest portion 31 b towards the closest portion 31 c. A shaft angle multiplier of 1× is applied to the resolver rotor 31 having the above configuration.

The outside diameter R1 of the first radial support member 14 a and the outside diameter R2 of the second radial support member 14 b are larger than an outside diameter R3 of an imaginary circle C1 that passes through the farthest portion 31 b and centers around the axial center L1 of the rotary shaft 14. A radius of the imaginary circle C1 represents a radius of gyration of the resolver rotor 31. Therefore, the radii of the first radial support member 14 a and the second radial support member 14 b are larger than the radius of gyration of the resolver rotor 31. The outside diameter R3 of the imaginary circle C1 is smaller than an outside diameter R4 of the motor rotor core 17 a. The outside diameter R1 of the first radial support member 14 a and the outside diameter R2 of the second radial support member 14 b are also smaller than the outside diameter R4 of the motor rotor core 17 a.

The following will describe the function of the centrifugal compressor 12 according to the first embodiment of the present disclosure.

In the centrifugal compressor 12 having the above configuration as shown in FIG. 2A, a rotating balance of the rotary shaft 14 is adjusted with the motor rotor 17 fixed to the rotary shaft 14 and the resolver rotor 31 fixed to the other end or the second end of the rotary shaft 14 before assembly of the rotary shaft 14 into the housing 13. The rotating balance of the rotary shaft 14 is adjusted by correcting an imbalance in a weight distribution of the circumferential direction of the motor rotor 17 or an imbalance in a weight distribution of the circumferential direction of the resolver rotor 31. After the rotating balance of the rotary shaft 14 is adjusted, the rotary shaft 14 is assembled into the housing 13.

The first radial bearing 21 is pre-fixed to an inside of a first housing constituent 41 that configures part of the housing 13 while the motor stator 18 and the second radial bearing 22 are pre-fixed to an inside of a second housing constituent 42 that configures part of the housing 13. The first housing constituent 41 and the second housing constituent 42 are to be connected to each other.

As shown in FIG. 2B, in order to assemble the rotary shaft 14 into the housing 13, the one end or the first end of the rotary shaft 14 opposite to the resolver rotor 31 is inserted into the inside of the first housing constituent 41. During the insertion, the one end or the first end of the rotary shaft 14 opposite to the resolver rotor 31 passes through the inside of the first radial bearing 21. Then, the rotary shaft 14 having the first radial support member 14 a surrounded by the first radial bearing 21 is assembled into the first housing constituent 41.

Then, the other end or the second end of the rotary shaft 14 at the side of the resolver rotor 31 is inserted into the inside of the second housing constituent 42. During the insertion, the resolver rotor 31 passes through an inside of the motor stator core 18 a because the outside diameter R3 of the imaginary circle C1 passing through the farthest portion 31 b and centering around the axial center L1 of the rotary shaft 14 is smaller than the outside diameter R4 of the motor rotor core 17 a while the second radial support member 14 b passes through the inside of the motor stator core 18 a because the outside diameter R2 of the second radial support member 14 b is smaller than the outside diameter R4 of the motor rotor core 17 a. In addition, the resolver rotor 31 passes through an inside of the second radial bearing 22 because the outside diameter R2 of the second radial support member 14 b is larger than the outside diameter R3 of the imaginary circle

Cl that passes through the farthest portion 31 b and centers around the axial center Li of the rotary shaft 14, that is, the radius of the second radial support member 14 b is larger than the radius of gyration of the resolver rotor 31. Then, the rotary shaft 14 is assembled into the second housing constituent 42 with the motor rotor 17 surrounded by the motor stator 18 as well as the second radial support member 14 b surrounded by the second radial bearing 22. In this way, the rotary shaft 14 is assembled into the housing 13.

According to the first embodiment of the present disclosure, the impeller 16 and the thrust support member 24 are fixed to the rotary shaft 14 after assembly of the rotary shaft 14 into the housing 13. Then, an unshown housing constituent that configures part of the housing 13 and to which the resolver stator 32 pre-fixed is connected to one end or the second end of the second housing constituent 42 opposite to the first housing constituent 41 with the resolver rotor 31 surrounded by the resolver stator 32.

The first embodiment of the present disclosure offers the effects described below.

-   (1-1) Because the rotary shaft 14 of the centrifugal compressor 12     rotates at a high speed of, for example, 80,000 rpm or more, a shaft     angle multiplier of 1× is applied to the resolver rotor 31 of the     resolver 30 of the first embodiment of the present disclosure for     accurate detection of the rotation angle of the motor rotor 17. The     smaller a shaft angle multiplier of the resolver rotor 31 is, the     greater the imbalance in the weight distribution in the     circumferential direction of the resolver rotor 31 becomes. The     rotary shaft 14 to which the resolver rotor 31 having a small shaft     angle multiplier is fixed may easily lose its rotating balance and     cause a runout.

In view of the above circumstances, the radius of the second radial support member 14 b is made larger than the radius of gyration of the resolver rotor 31. Accordingly, during assembly of the rotary shaft 14 into the housing 13, the resolver rotor 31 may pass through the inside of the second radial bearing 22 with the motor rotor 17 fixed to the rotary shaft 14 and the resolver rotor 31 fixed to the other end or the second end of the rotary shaft 14 opposite to the impeller 16 before assembly of the rotary shaft 14 into the housing 13. Therefore, the rotating balance of the rotary shaft 14 is adjusted by correcting an imbalance in a weight distribution of the circumferential direction of the motor rotor 17 or the resolver rotor 31 with the motor rotor 17 and the resolver rotor 31 fixed to the rotary shaft 14 before assembly of the rotary shaft 14 into the housing 13. In other words, the rotary shaft 14 is assembled into the housing 13 after adjustment of the rotating balance of the rotary shaft 14 with the resolver rotor 31 fixed to the rotary shaft 14. As a result, the runout of the rotary shaft 14 may be suppressed.

Second Embodiment

The following will describe a centrifugal compressor 12 according to a second embodiment of the present disclosure with reference to FIGS. 3 to 4B. In the description of the second embodiment below, duplicated descriptions of configurations identical with those of the first embodiment of the present disclosure described above will be omitted or simplified by, for example, providing the identical reference numerals.

As shown in FIG. 3, an outside diameter R1 of a first radial support member 14 a and an outside diameter R2 of a second radial support member 14 b are larger than an outside diameter R4 of a motor rotor core 17 a and smaller than an inside diameter R5 of a motor stator core 18 a.

The following will describe the function of the centrifugal compressor 12 according to the second embodiment of the present disclosure.

In the centrifugal compressor 12 having the above configuration as shown in FIG. 4A, the rotating balance of a rotary shaft 14 is adjusted with a motor rotor 17 and a resolve rotor 31 fixed to the rotary shaft 14 as well as a thrust support member 24 fixed to the rotary shaft 14 before assembly of the rotary shaft 14 into a housing 13. Two thrust bearings 23 are supported by the thrust support member 24. After the rotating balance of the rotary shaft 14 is adjusted, the rotary shaft 14 is assembled into the housing 13.

A first radial bearing 21, a motor stator 18, and a second radial bearing 22 are pre-fixed to an inside of a housing constituent 43 that configures part of the housing 13.

As shown in FIG. 4B, in order to assemble the rotary shaft 14 into the housing 13, the other end or the second end of the rotary shaft 14 on the side of a resolver rotor 31 is inserted into the inside of the housing constituent 43. During the insertion, the resolver rotor 31 passes through the inside of the first radial bearing 21 because the outside diameter R1 of the first radial support member 14 a is larger than an outside diameter R3 of an imaginary circle C1 that passes through a farthest portion 31 b and centers around an axial center L1 of the rotary shaft 14, that is, the radius of the first radial support member 14 a is larger than the radius of gyration of the resolver rotor 31. The resolver rotor 31 passes through an inside of the motor stator core 18 a because the outside diameter R3 of the imaginary circle C1 is smaller than the outside diameter R4 of the motor rotor core 17 a. The resolver rotor 31 passes through an inside of a second radial bearing 22 because the outside diameter R2 of the second radial support member 14 b is larger than the outside diameter R3 of the imaginary circle C1, that is, the radius of the second radial support member 14 b is larger than the radius of gyration of the resolver rotor 31.

The second radial support member 14 b passes through the inside of the first radial bearing 21. Then, the second radial support member 14 b passes through the inside of the motor stator core 18 a because the outside diameter R2 of the second radial support member 14 b is larger than the outside diameter R4 of the motor rotor core 17 a and smaller than the inside diameter R5 of the motor stator core 18 a. In addition, the motor rotor core 17 a passes through the inside of the first radial bearing 21 because the outside diameter R1 of the first radial support member 14 a is larger than the outside diameter R4 of the motor rotor core 17a. The rotary shaft 14 is assembled into the housing constituent 43 with the first radial support member 14 a surrounded by the first radial bearing 21, the motor rotor 17 surrounded by the motor stator 18, and the second radial support member 14 b surrounded by the second radial bearing 22. In this way, the rotary shaft 14 is assembled into the housing 13.

According to the second embodiment of the present disclosure, the :30 impeller 16 is fixed to the rotary shaft 14 after assembly of the rotary shaft 14 into the housing 13. Then, an unshown housing constituent that configures part of the housing 13 and to which a resolver stator 32 is pre-fixed is connected to one end of the housing constituent 43, or the second end, opposite to the impeller 16 with the resolver rotor 31 surrounded by the resolver stator 32.

The second embodiment of the present disclosure offers the effects described below in addition to the effects equivalent to those (1-1) of the first embodiment.

(2-1) The outside diameter R1 of the first radial support member 14 a and the outside diameter R2 of the second radial support member 14 b are larger than the outside diameter R4 of the motor rotor core 17 a and smaller than the inside diameter R5 of the motor stator core 18 a. Accordingly, during assembly of the rotary shaft 14 into the housing 13, the second radial support member 14 b passes through the inside of the motor stator core 18 a, and the motor rotor core 17 a passes through the inside of the first radial bearing 21 with the motor rotor 17 and the resolver rotor 31 fixed to the rotary shaft 14 before assembly of the rotary shaft 14 into the housing 13. Therefore, during assembly of the rotary shaft 14 into the housing 13, the other end or the second end of the rotary shaft 14 at the side of the resolver rotor 31 passes through the inside of the first radial bearing 21, the inside of the motor stator core 18 a and the inside of the second radial bearing 22.

Therefore, the thrust support member 24 is disposed closer to the impeller 16 than the resolver rotor 31, the motor rotor 17, the first radial support member 14 a, and the second radial support member 14 b in the axial direction of the rotary shaft 14. For this reason, the rotary shaft 14 that has the thrust support member 24 before assembled into the housing 13 may be assembled into the housing 13. Therefore, the rotating balance of the rotary shaft 14 may be adjusted by correcting an imbalance in the weight distribution of the circumferential direction of the motor rotor 17 or the resolver rotor 31 with the motor rotor 17 and the resolver rotor 31 fixed to the rotary shaft 14 before assembly of the rotary shaft 14 into the housing 13 and with the rotary shaft 14 having the thrust support member 24.

The following modifications may be made to the first and second embodiments described above. The embodiments above and the following modifications may be combined one another unless otherwise fallen into technical inconsistency.

In the above embodiments, a shaft angle multiplier of 2× or 3× or larger may be applied to the resolver rotor 31.

In the above embodiments, the first radial bearing 21 and the second radial bearing 22 may be a sliding bearing or a rolling bearing.

In the above embodiments, the centrifugal compressor 12 may be used for compressing fluid other than oxidant gas to supply to the fuel cell stack 11 of the fuel cell system 10. For example, the centrifugal compressor 12 may compress refrigerant as fluid used for an air conditioning system.

In the above embodiments, the fuel cell system 10 may be mounted onto an object other than a vehicle. 

What is claimed is:
 1. A centrifugal compressor comprising: a housing; a rotary shaft accommodated in the housing; an electric motor rotating the rotary shaft, the electric motor including a motor rotor fixed to the rotary shaft and a motor stator fixed to the housing; an impeller connected to one end of the rotary shaft and driven by rotation of the rotary shaft so as to compress fluid; a radial bearing rotatably supporting the rotary shaft in a radial direction of the rotary shaft in relation to the housing; and a resolver detecting a rotation angle of the motor rotor, the resolver including a resolver rotor fixed to the rotary shaft and a resolver stator fixed to the housing, wherein the resolver rotor is fixed to the other end of the rotary shaft opposite to the impeller, the rotary shaft includes a radial support member rotatably supported by the radial bearing, and a radius of the radial support member is larger than a radius of gyration of the resolver rotor.
 2. The centrifugal compressor according to claim 1, further comprising: a thrust bearing rotatably supporting the rotary shaft in an axial direction of the rotary shaft in relation to the housing, wherein the rotary shaft includes a thrust support member rotatably supported by the thrust bearing, the thrust support member is disposed at the rotary shaft closer to the impeller than the resolver rotor, the motor rotor, and the radial support member in the axial direction of the rotary shaft, and an outside diameter of the radial support member is larger than an outside diameter of the motor rotor core of the motor rotor and smaller than an inside diameter of the motor stator core of the motor stator.
 3. The centrifugal compressor according to claim 1, wherein a shaft angle multiplier of 1× or 2× is applied to the resolver rotor. 